Cost Per Mille (CPM) — also known as cost per thousand — is a marketing metric denoting the cost of 1,000 advertisement impressions on a web page. For instance, if a web publisher charges $3.00 CPM, an advertiser pays the publisher $3.00 per 1,000 impressions of its ad. In CPM, the "M" stands for "mille," which is Latin for "thousand." Put simply, Cost per Mille (CPM) is the cost paid per 1000 impressions of your digital ads. Google refers to it as viewable CPM — or vCPM — which means that at least 50% of your ad needs to display on screen for a minimum of one second. That, according to Google, qualifies as an impression. Regarding video CPM, your video needs to play for at least two seconds to register as an impression. You read that correctly — even clicking "Skip video" after three seconds counts as a view.In this display advertising model on Google, you don't pay for clicks on your ad — as with Cost-Per-Click (CPC) — instead, you only pay for the number of times it is displayed. In other words, if you're confident that your ad has the potential to drive click-throughs, you could stretch your ad budget further by opting for the CPM model.Bear in mind, that a thousand impressions can rack up quickly, meaning that the publisher will charge you every time every member of the audience views your ad. In other words, if an individual views your ad ten or twenty times in a day, each of those views, or impressions, accumulates toward your total CPM. It's conceivable that they could see your ad a hundred times or more and not once click on it.Cost per thousand (CPM) is the most prevalent protocol for pricing ads in digital marketing. The method focuses on impressions — ad views — representing the number of views or engagements for a particular digital advertisement. Advertisers pay website owners a pre-determined fee per one thousand ad impressions. Although an impression measures the number of times a site displays the ad — it does not measure whether viewers clicked the ad.